Resin particles having a large particle diameter and high monodispersity are required as light-diffusing agents of light-diffuser films, light-diffuser plates, anti-glare films, and the like constituting display devices like liquid crystal TVs (televisions); additives for various mat materials; additives for paints; spacers; anti-blocking agents; chromatography fillers; and carriers for diagnostic reagents.
Seed polymerization techniques are known as processes for producing such resin particles. A seed polymerization technique is a process in which seed particles comprising a polymer having a uniform particle diameter are prepared in advance in an aqueous medium, and then a monomer is absorbed into the seed particles and polymerized (for example, Japanese Unexamined Patent Application, First Publication No. H08-169907; Patent Document 1). Absorption and polymerization of the monomer are normally repeated until resin particles having the desired particle diameter are obtained. In seed polymerization techniques, a water-soluble polymer dispersant having excellent dispersibility such as polyvinyl alcohol is mainly used as the dispersant.
However, it is easy for the water-soluble polymer dispersant such as polyvinyl alcohol to remain in resin particles. When the water-soluble polymer dispersant remains in resin particles, there is the problem of discoloration (yellowing) of resin particles by heat of the water-soluble polymer dispersant such as polyvinyl alcohol and deterioration over time. In order to prevent discoloration of resin particles by heat and the like, carrying out washing after polymerization in order to remove the water-soluble polymer dispersant such as polyvinyl alcohol can be considered. However, since it is difficult to completely remove the water-soluble polymer dispersant by washing, resin particles obtained using a water-soluble polymer dispersant include residual water-soluble polymer dispersant and thus yellowing when heated cannot be avoided. Also, when washing is carried out in order to remove the water-soluble polymer dispersant, there is the problem that productivity decreases since time for washing the resin particles is required.
Thus, a process for producing resin particles not using polyvinyl alcohol by using a specific surfactant has been suggested in Japanese Unexamined Patent Application, First Publication No. H10-298250 (Patent Document 2).